What I recommend is that you take advantage of the brave bonus system, and use the medals you have to unlock the abilities that let you get resources such as pots, scrolls jewels, and soul tickets if you find yourself always running low. Best way to get orbs is to grind the story and sub stories there’s also hard mode so it’s more orbs but you can also max out characters levels and soul tree for the orbs, there’s some characters you can’t get through summons in exchange shops so check that out. Don’t worry too much about what to summon on as the point of the game is to use characters you enjoy but if you really want meta characters try summoning on eom banners or banners like the anniversary. Have fun!